Abstract:
The synthesis as well as structural, magnetic, optical and photocatalytic properties of
sillenite and perovskite type undoped and Gd-doped bismuth ferrite-reduced graphene
oxide (BiFeO3-rGO) nanocomposites have been investigated. Graphite oxide was
initially prepared using modified Hummer’s method, followed by hydrothermal
synthesis of the nanocomposites at different reaction temperatures. The X-ray
diffraction measurements confirmed the formation of perovskite type BiFeO3-rGO
composites at a reaction temperature of 2000C which is the lowest temperature for the
formation of this phase, However, a structural transition to sillenite type (Bi25FeO40)
was observed at 1800C. Such phenomenon is notable since simply by tweaking the
temperature by 200C, composite of desired phase of bismuth ferrite with rGO may be
formed keeping all other conditions same. The FESEM images demonstrated that the
particle size of the perovskite nanocomposites was ∼25-60 nm, and for the sillenite
phase composites it was ∼10-30 nm. With Gd doping, similar phases were obtained,
however, impurity phases were present and the particles were of larger size. The assynthesized
composites exhibited significantly enhanced saturation magnetization
over pure BiFeO3 nanoparticles, with Bi25FeO40-rGO composite having higher
saturation magnetization than all other samples. Among the Gd-doped composites, the
perovskite phase provided higher magnetization compared to the sillenite one which
might be attributed to the impurities involved. The optical characteristics of the
nanocomposites demonstrated considerably higher absorbance in the visible range
with significantly lower band gap in comparison to pure BiFeO3. Again, sillenite type
Bi25FeO40-rGO composite was found to have lower bandgap compared to the
perovskite counterpart. In this case, higher bandgaps were obtained for the Gd-doped
composites in comparison with the undoped composites which may be due to larger
particle size of the doped samples. Next, the photocatalytic and H2 production
experiments were investigated. The photocatalytic efficiency of a material depends on
its bandgap, surface morphology and particle size distribution. Keeping this in mind,
undoped perovskite and sillenite composites were chosen for experimentation as these
provided the most promising relevant properties. The composites provided higher
photocatalytic efficiency and stability than pure bismuth ferrite and between the
composites, sillenite Bi25FeO40-rGO once again provided enhanced performance. This
composition demonstrated higher H2 production results among all the samples,
notably providing 3.5 times enhancement over commercially available TiO2. The
present investigation provides a means of selective transition as desired between
composites of rGO with perovskite and sillenite phase bismuth ferrite by temperature
control and the results suggest that incorporation of graphene with sillenite type
bismuth ferrite provides enhanced performance in terms of all the properties
investigated. Moreover, composites of rGO with 10% Gd-doped bismuth ferrites did
not provide enhancements in the properties and further investigations are necessary to
improve the properties of the rare earth doped bismuth-rGO nanocomposites.
